New context with albums and lyrics +++ much more

* Added new lyrics provider with lyrics from AudD and API Seeds
* New improved context widget with albums and lyrics
* Fixed playing and context widget getting stuck in play mode when there was an error
* Changed icons for artists in collection, tidal and cover manager
* Removed "search" icon from "Search automatically" checkbox (right click) that looked ugly
* Removed some unused widgets from the src/widgets directory
* Fixed initial size of window and side panel
* Fixed saving window size correctly

src/lyrics/lyricsproviders.h

@@ -0,0 +1,60 @@
+/*
+ * Strawberry Music Player
+ * Copyright 2018, Jonas Kvinge <jonas@jkvinge.net>
+ *
+ * Strawberry is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Strawberry is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Strawberry.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#ifndef LYRICSPROVIDERS_H
+#define LYRICSPROVIDERS_H
+
+#include "config.h"
+
+#include <stdbool.h>
+
+#include <QtGlobal>
+#include <QObject>
+#include <QMutex>
+#include <QList>
+#include <QMap>
+#include <QString>
+#include <QAtomicInt>
+
+class LyricsProvider;
+
+class LyricsProviders : public QObject {
+  Q_OBJECT
+
+ public:
+  explicit LyricsProviders(QObject *parent = nullptr);
+  void AddProvider(LyricsProvider *provider);
+  void RemoveProvider(LyricsProvider *provider);
+  QList<LyricsProvider*> List() const { return lyrics_providers_.keys(); }
+  bool HasAnyProviders() const { return !lyrics_providers_.isEmpty(); }
+  int NextId();
+
+ private slots:
+  void ProviderDestroyed();
+
+ private:
+  Q_DISABLE_COPY(LyricsProviders);
+
+  QMap<LyricsProvider *, QString> lyrics_providers_;
+  QMutex mutex_;
+
+  QAtomicInt next_id_;
+};
+
+#endif  // LYRICSPROVIDERS_H